In Q&A Profile Settings | Security Settings, if "Hide users' answers by default" is checked then the user is asked to confirm each answer when registering.
However if the user puts the correct answer in the first answer field and then puts an incorrect answer in confirmation field, PM accepts it without checking one answer against the other.
This is a product defect.
A permanent fix is scheduled to be included in Password Manager 5.6.2. A public hotfix is also available for 5.6.1:
Password Manager 5.6.1 Public Hotfix - During user registration Password Manager accepts not matched answers (181503)